Alternating current machines

ABSTRACT

An AC generator comprises a rotor  25  within a stator  24 . The rotor carries a fan  27  at one end of the stator. The fan  27  is within a casing  30  which forms volute discharge passages  32 . The fan  27  has blades  31  which project from the hub  28  at an angle which is oblique to the radial whereby those blades  31  trail the radial. The stator windings  23  form terminal leads  34  which are led from the end of the stator  24  remote from the fan  27 . A circumferential array of cleats  35  which each have the form of a comb, support and guide the terminal leads  34  circumferentially, spaced from one another, to a certain location at the top from which the leads are taken and connected to terminals above. Those terminals are formed by the lower ends of busbars ( 56  to  58, 61  to  69 ) which extend through and which are supported by a structural panel of insulating material which forms an insulating barrier between the ends of those busbars. The upper end of each of those busbars forms the power output terminals U, V and W and the neutral terminals of the machine.

[0001] This invention relates to an alternating current machine and moreparticularly although not exclusively to an AC generator.

[0002] An alternating current machine comprises a rotor journalled forrotation within a stator comprising stator windings which are gatheredtogether into an annular array at either end of the stator. The statorwindings may be perfect lap windings or perfect concentric windings.Either way they comprise handles of generally parallel conductors whichare led from end to end of the stator and turned around at either end soas to be led back along the length of the stator. The bundles ofconductors are led from end to end of the stator along generallyparallel paths and form pairs of terminal leads at either end, theterminal leads being taken from one end of the stator to neutral andpower output terminals of the machine to which they are connected.

[0003] It the terminal leads are bunched together as a solid mass,problems with hot spots arise. Also difficulties arise which cause theterminals to which terminal leads are connected to be located wellspaced from the axis of rotation of the rotor. In practice there is noinsulation between those terminals and the annular array of statorwindings of the machine as is shown in DE-A-1144382.

[0004] U.S. Pat. No. 5,175,458 discloses an assembly for carrying statorterminal leads to a terminator to which an electrical connection can bemade. The alternator for which this assembly is designed is relativelysmall. The assembly comprises an arcuate, or horseshoe-shaped memberwhich is fitted to the appropriate end of the stator. Thehorseshoe-shaped member is solid and has three circumterentiallyextending channels defined in its outer surface. Each channel receives aterminal lead which is an extension of a stator winding and leads thatterminal lead along the circumferentially extending track it forms tothe terminator to which it is connected. The channels are axially spacedfrom one another. This arrangement would suffer from cooling problems ifit were to be used in large alternating current machines because theterminal leads would be shielded from cooling air flow through thestator.

[0005] According to one aspect of this invention there is provided analternating current machine as claimed in claim 1 Preferred features ofthat alternating current machine are claimed in claims 2 to 24.

[0006] DE-A-1144382 illustrates an arrangement of output terminals of analternating current machine to which stator winding terminal leads maybe connected. Each terminal to which such a terminal lead is connectedis supported by a metal angle member to which it is riveted. The anglemembers are spaced from one another and are mounted at either end on asupport fixed to the casing through a respective insulator. Theelectromagnetic forces that can be generated under fault conditions,such as sudden or sustained short circuit faults externally imposed anthe machine by the power transmission or distribution system to which itmay be connected, can cause the angle members to which the terminals areriveted to twist and in the extreme case, cause adjacent terminals tocontact one another with undesirable consequences.

[0007] FR-A-2693848 disclosed a mounting for distribution busbars inwhich the busbars are clamped between elongate mouldings which fillspaces between faces of adjacent busbars. The mouldings have a uniformcross-section with flat sides which are in face to face abutment withthe faces of the busbars. Gaps remain between the edges of adjacentbusbars and adjacent mouldings since the mouldings are spaced from oneanother by the thickness of the busbars. The stack of mouldings andbusbars is clamped by nuts fitted to the ends of screws which extendthrough the gaps and through aligned holes in the mouldings.

[0008] According to another aspect of this invention there is provided aterminal arrangement for leads from stator windings of an alternatingcurrent machine as claimed in claim 25. Preferred features of thatterminal arrangement are claimed in claims 26 and 27.

[0009] It is desirable to arrange the busbars of the terminalarrangement of a three phase machine so that the leads can be connectedto their portions below the structural panel permanently and adjustmentbetween a series star connection and parallel star connection can bemade from above the structural panel without altering the connection ofthe leads below. This is achieved by providing for each of the threepower output busbars and the respective neutral busbars, a respectivepair of spaced busbars which extend through the structural panel insubstantially the same way as the neutral and power output busbarsbetween which they are located. Each such respective pair of spacedbusbars are connected together by a suitable link above the structuralpanel for a series star connection. On the other hand, one busbar ofeach such respective pair is connected to the adjacent neutral busbarand the other busbar of the respective pair is connected to the adjacentpower output busbar for a parallel star connection, such connectionsbetween the busbars being made by suitable links above the structuralpanel.

[0010] The rotor of an alternating current machine may carry a fan atthe end of the stator remote from the terminal leads. The fan would beoperable to draw air through the stator from the remote end therof inorder to cool the stator windings.

[0011] DE-A-2526532 discloses such a rotor and fan arrangement. The fanis within a casing which cooperates with it to provide a conduit fordischarge of air flow from the fan, the conduit being in the form of avolute whereby its area increases progressively in the downstreamdirection. Although such use of a volute casing improves the cooling byincreasing the volume of air that is drawn through the stator by the fanfor discharge through the discharge passage formed by the volute casing,even more cooling is desirable.

[0012] According to a further aspect of this invention Lhere is providedall alternating current machine according to claim 28. Preferredfeatures of that alternating crrent machine are claimed in claims 29 to31.

[0013] A three phase AC generator which embodies this invention andcertain modifications thereof will be described now by way of examplewith reference to the accompanying drawings, of which:

[0014]FIG. 1. is a side elevation of the AC generator with part of thecasing cut away;

[0015]FIG. 2. is an end elevation of the AC generator as seen in thedirection of arrow A in FIG. 1;

[0016]FIG. 3. is a sectioned view of the right hand end part of the ACgenerator as shown in FIG. 1 which includes a fan, the section being onthe line III-III in FIG. 2;

[0017]FIG. 4. is a section on the line IV-IV of FIG. 1 showing the fanwithin its casing;

[0018]FIG. 5. is a side elevation drawn to a larger scale than is shownin FIG. 1, of the upper part of the stator of the AC generator shown inFIG. 1 and as seen in the direction of arrow C in FIG. 6, with thewindings that emerge from it at either end and the arrangement of outputleads at the left hand end, a modification of the latter being shownchain dotted;

[0019]FIG. 6. is a partly sectioned end elevation of the stator shown inFIG. 5 to a larger scale, the section being on the line VI-VI in FIG. 5;

[0020]FIG. 7. is a fragmentary view showing one of the circumferentialarray of cleats shown in FIGS. 5 and 6, mounted on a group of lapwindings at the left hand end of the stator as shown in FIG. 5;

[0021]FIG. 8. is a section on the line VIII-VIII in FIG. 6, to a largerscale than in FIGS. 5 and 6;

[0022]FIG. 9. is a view in elevation of the terminal block as showndotted in FIG. 1, to a larger scale and in more detail;

[0023]FIG. 10. is a side view of the terminal block shown in FIG. 9 asseen along arrow B in FIG. 1;

[0024]FIG. 11. is a view in perspective from the underside of theterminal block of the AC generator as shown in FIGS. 1, 9 and 10;

[0025]FIG. 12. is a perspective view from above of the terminal blockshown in FIG. 11;

[0026]FIG. 13. is a diagrammatic cross section of stator windingsarranged in a “perfect” concentric configuration:

[0027]FIG. 14. is a section on the line XIV-XIV In FIG. 13 of windingsin a longitudinally extending groove in the inner surface of the stator:and

[0028]FIGS. 15 and 16 are views similar to FIGS. 6 and 8 respectively ofthe modified form of the AC generator shown in FIGS. 1 to 14 which inillustrated in chain dotted lines in FIG. 5, FIG. 16 being a section onthe line XVI-XVI in FIG. 15.

[0029]FIGS. 1 and 2 show an AC generator which comprises a casing 21. Atthe left hand of the casing 21, as seen in FIG. 1, there is an outputterminal block 22 by which a three phase alternating current generatedby the AC generator is collected from armature windings 23 (see FIG. 1)on a stator 24 which is housed within the casing 21. A rotor 25 isjournalled in the stator 24. The rotor 25 carries a coupling plate 26 atits right hand end, as seen in FIG. 1. The coupling plate 26 is forcoupling to a fly-wheel of a prime mover or engine whereby the rotor 25is driven.

[0030]FIG. 3 shows the right hand end of the rotor 25 projecting fromthe right hand end of the stator 24 A radial flow fan 27 is bolted ontoa hub 28 which is force fitted onto the end of the rotor 25 adjacent thecoupling plate 26 which is fixed to it by set screws 29. The fan 27 maybe forced fitted directly onto the rotor 25 instead.

[0031]FIGS. 3 and 4 show the fan 27 is surrounded by a volute casing 30which is bolted to the end of the casing 21. The volute casing 30 isformed so that two diametrically opposed portions of it diverge in thedownstream direction from the path traced by the tips of the blades 31of the fan 27. Hence two diametrically opposed passages 32 for thedischarge of air from the fan 27 are formed between the fan 27 and thevolute casing 30, the cross-sectional area of each of these dischargepassages 32 increasing progressively in the discharge direction.

[0032] Each blade 31 projects from the hub 28 at an angle which isoblique to the notional radius that passes through the root of thatblade 31, each blade 31 diverging from its respective notional radius ina direction which is upstream with respect to air flow generated by thefan 27. The tip 33 of each blade 31 is tapered so that it converges withthe axis of rotation, the angle of taper being of the order of 12.5degrees and the taper being towards the coupling plate 26.

[0033]FIG. 5 shows the stator 24 with the casing 21 and the rotor 25removed. The stator windings 23 may be either perfect lap windings orperfect concentric windings as will be understood by a man skilled inthe art.

[0034] The conductors that form the stator windings 23 are extendedoutwards from the left hand end of the stator 24, as seen in FIG. 5, toform leads 34 by which the stator windings 23 are connected to theterminal block 22. Each lead 34 and the respective stator winding 23 towhich it is connected is a one pierce conductor without any electricalconnection joining them together. The leads 34 project from the stator24 initially as an axially extending circumferentially spaced array.There are twelve pairs of such leads 34, each pair being extensions ofthe opposite ends of a respective one of the stator windings 23 andbeing angularly spaced from one another by about 155°.

[0035] A circumferential array of cleats 35 project from the end of thestator sore on which they are mounted. FIG. 6 shows that one of thecleats 35 is located at the top of the stator 24 and the others areequally spaced at angular intervals of about 30°.

[0036]FIG. 7 shows an exemplary group of stator windings 23 at the endof the stator 24 from which the power output leads 34 are led to theoutput terminal block 22. Each winding 23 comprises a bunch of generallyparallel wire conductors 36 which are led along generally parallel pathswhich run the length of the stator 24 from end to end and which areturned around at either end, so that a bunch of wire conductors 36 whichemerges from one axially extending path in the stator 24 at one end ofthe stator 24 is turned around to re-enter a parallel axially extendingpath in the stator 24. These windings 23 are a perfect lap windingarrangement so that each curved winding portion 37 by which the wireconductors 36 are so turned around overlap several of the adjacentcurved winding portions 37 that are spaced from it in onecircumferential direction around the stator 24, those being the otherwinding portions 37 that emerge from the stator 24 between its point ofemergence from the stator 24 and its point of re-entry to the stator 52.Also, there are two bunches of conductors 36 laid one on the other ineach parallel path in the stator 24. All the reentrant conductors 36 arelaid over the other bunch of conductors 36 that they overlap, in therespective path. Each of these windings 23 has two ends which areextended outwards from the stator 24 to form the power output leads 34by which the stator windings 23 are connected to the terminal block 22.

[0037] Each cleat 35 is a moulding of an electrically insulatingplastics material such as nylon. FIG. 3 shows that each cleat 35comprises an elongate back portion 39 from which seven prongs 41 projectlaterally so that it has the form of a comb. Each cleat 35 is mounted onthe stator core with its back portion 39 extending axially with respectto the stator 24 and with the prongs 41 projecting radially outwardly.The prongs 41 are shaped so that the nearer sides of juxtaposed prongs41 converge. Hence each of the intervening spaces of each cleat 35 isthereby adapted to receive a lead 34 which is fitted into it with a snapaction through its narrow mouth and which is retained in it by theprongs 37. Two spaced walls 42 project from the back portion 39 in theopposite direction to that in which the prongs 41 project, each sidewall 42 extending from a respective one of the two longitudinallyextending edges of the hack portion 39. The spacing between the two sidewalls 42 is bridged at one end of the cleat 35 by a flat plate-likeelement 43 at the ends of the side walls 42 remote from the back portion39, the plate-like element 43 projecting from the end of the side walls42 to form a projecting tongue 44. The space between the side walls 42is also bridged by another short plate-like portion 45 at a locationwhich is about three-quarters of the length of the cleat 35 from theplate-like element 43. The thickness of the plate-like portion 45increases progressively in the direction away from the plate-likeelement 43, flaring outwardly from the back portion 39 to the end whichis remote from the plate-like element 43.

[0038] The outer end of each prong 41 has a rectangular recess 46 formedin it substantially centrally. The recesses 46 in each prong 41 arealigned. Each cleat 35 is provided with a respective strap 47 by whichit is fastened to the adjacent group of curved stator winding portions37. The strap 47 has a rectangular cross-section and is provided at oneend with a ring portion 48 which serves as a retaining socket, theaperture of the socket having a similar form, it being for receiving theother end of the strap 47. One of the sides of the strap 47 is providedwith formations which engage in a corresponding formation in the innerperiphery of the ring portion 48 whereby the length of strap 47 threadedthrough the aperture of the ring portion 48 is retained therein againstbeing pulled back.

[0039] The strap 47 is laid in the recesses 46 at the ends of the prongs41 so that it projects from either end of the cleat 35, the ring portion48 being to the left as seen in FIG. 8. The ring portion 48 is threadedinto the channel between the side walls 42 and through the gap betweenthe back portion 39 and the plate-like element 43. From there it isdrawn through the gap between the plate-like element 43 and theplate-like portion 45 and passed around the plate-like portion 45 to theother end of the cleat 35 where it is fitted over the other end of thestrap 47 which protrudes from the cleat 35 so as to complete a loopformed by the strap 47 which surrounds the cleat 35.

[0040] The flared plate-like portion 45 rests upon the adjacent curvedstator winding portion 37 and the tongue 44 locates against the end ofthe stator 24. The curved winding portions 37 that are below the cleat35 are encircled by the strap 47 so that they are trapped between thestrap 47 and the lower edges of the side walls 42 of the cleat 35whereby the cleat 35 is fastened to them.

[0041] The length of the strap 47 which is laid within the recesses 46in the prongs 41 serves to brace leads 34 within the respectiveintervening spaces between juxtaposed prongs 41 through which they areled from the stator windings 23 to the terminal block 22 to resistelectromagnetic forces, which would otherwise tend to displace them,especially under fault conditions, such as sudden or sustained shortcircuit faults, externally imposed on the alternator by the powertransmission or distribution system to which it may be connected. Theprongs also serve as spacers which space juxtaposed terminal leads 34apart and react electromagnetic forces which act to urge towards themthe leads 34 that they separate.

[0042] The strap 47 is a moulding of electrically insulating plasticsmaterial such as nylon.

[0043] The six radially outwardly tapered spaces formed between theprongs 41 of each of the cleats 35 are arranged as a circumferentiallyspaced series and thereby define six juxtaposed circumferential tracksfor the leads 34 by which those leads 34 are guided from the stator 24to a location to one side of and above the stator 24 at which theyterminate as an array of twenty four upwardly projecting terminals 49.This can be seen in FIGS. 1, 5 and 6. FIGS. 1 and 5 show that the leads34 are spaced from one another in the direction of the axis of thestator 24 as they are led side by side around the six circumferentiallyextending tracks formed by the cleats 35. The circumferential array ofcleats 35 and the leads 34 they guide around the circular path togetherform a grid structure so that those leads 34 are supported in free spaceby the cleats 35. Also the interstices of that grid structure serve asventilation spaces through which air can be drawn past the leads 34 sothat the latter are cooled. The linking together of the circumferentialarray of cleats 35 by the leads 34 into the grid structure providesadditional strength to resist the effect of electromagnetic forceswhich, as previously described, would tend to displace the leads 34 andthe protruding windings 23 under fault conditions, and thus augments theresistance to such electromagnetic forces provided by the straps 47 ofeach individual cleat 35 of the array.

[0044]FIG. 6 shows the arrangement of the four leads 34A and B and 34Cand D that are led around an exemplary one of the circumferentiallyextending tracks, that being the track that is formed by those spaces ofthe cleats 35 that are nearest to the stator 24. The lead 34A extendsaxially from the stator 24 at a location which is spaced angularly fromthe top of the stator 24 by a few ° so that it is just to the right ofthe cleat 35T at the top, as seen in FIG. 6. From there it is benttowards and snap-fitted into that cleat 35T from which it is bentupwards to its terminal 49. The lead 34B, which is the other of therespective pair of leads 34 that are extensions of the opposite ends ofa respective one of the stator windings 23, extends axially from thestator 24 at a location which is spaced angularly from the bottom of thestator 24 by about 25°. It is bent towards and snap-fitted into therespective space in the cleat 35A that is spaced from the bottom of thestator 24 by 30° and to the right as seen in FIG. 6. The lead 34B isthen snap-fitted into the respective space in each of the other fourcleats 35B-35E on the same side of the stator 24 and finally it issnap-fitted into the cleat 35T above the lead 34A as can be seen fromFIG. 6 The lead 34B is then bent upwards to its terminal 49 alongsidethe lead 34A.

[0045] The lead 34C emerges axially just to the left of the bottom cleat35L. This is bent towards and snap-fitted into the respective space inthe cleat 35F that is spaced from the bottom of the stator 24 by 25° andto the left as seen in FIG. 6. It is then snap-fitted into thecorresponding space in each of the other four cleats 35G to 35K on thesame side of the stator 24. The other lead 34D of the respective pairemerges axially from the stator 24 just to the right of the cleat 35K.The two leads 34C and 34D are then bent together upwards to theirrespective terminals 49 alongside the pair of leads 34A and 34B.

[0046] It will be understood that each of the six tracks leads arespective group of two pairs of leads 34 so that they extend upwardlyto their terminals 49 in a manner similar to that described above withreference to FIG. 6.

[0047] Cleats having only four spaces instead of the six described andillustrated for the cleats 35 are used in single phase AC generators ofotherwise similar design. FIGS. 9 and 10 show that the terminal block 22comprises a structural panel 51. This panel 51 is formed of six similarelongate angle members 52A to 52F which are arranged in three juxtaposedpairs. The upright faces 53A and 53B, 53C and 53D, 53E and 53F, areabutting and the adjacent edges of the horizontal sides of juxtaposedangle members 52A to 52F are also abutting so that the six angle members52A to 52F present a substantially continuous uninterrupted surface atthe bottom of the terminal block 22. Each pair of abutting faces 53A-53Fof each pair of angle members 52A and 52B, 52C and 52D, 52E and 52F,have opposed grooves 54 and 55 formed in them running substantiallyvertically from the top to the bottom. There are four such grooves 54and 55 formed in each of those abutting faces 53A-53F. They are spacedapart along the length of the respective angle members 52A to 52F to thesame extent. The outer pair 54 of these four grooves are each abouttwice as long as each of the inner pair 55 of those grooves. Eachopposed pair of grooves 54 and 55 in the abutting faces 53A-53F forms arectangular section through passage running between the top and thebottom of the abutting vertical faces 53A-53F of the abutting anglemembers 52A-52F.

[0048] Each such a through passage receives a respective busbar 56-58,61-69 which is a close fit therein. The twelve busbars 56-58, 61-69depend below the panel 51 spaced one from another, as can be seen inFIG. 11, and each provides a terminal connection to which a respectiveterminal 49 of the leads 34 from the stator windings 23 is connected.Each of these busbars 56-58, 61-69 also projects above the panel 51.

[0049] Each of the angle members 52 is formed from an insulatingstructural plastics material, such as nylon, by moulding.

[0050] The group of three busbars 56-58 that extend through the threeleft hand larger through passages 54, as seen in FIGS. 11 and 12, eachprovides a respective one of the three output terminals U, V and W forthe three phase supply generated by the three phase AC generator. Thethree busbars, 61-63, of the other group that extend through the threeright hand larger through passages 54, as seen in FIGS. 11 and 12 arebent over at 90° above the panel 51 and are each connected to a commonbusbar 71 which provides the neutral output terminal of the ACgenerator.

[0051] The two further groups of three separate busbars 64-66 and 67-69that are provided between the three busbars 56-58 which serve as thethree output terminals U, V and W and the other three busbars 61-63 thatare connected together to the neutral output terminal 71, are spacedfrom each other and from those other busbars 56-58, 61-63 so as to beelectrically insulated therefrom by the electrically insulating materialof the structural panel 51. Each of the busbars 64-69 is located withina respective rectangular through passage which is formed by appropriateones of the smaller grooves 55 in the abutting faces 53 of the anglemembers 52. Each of these two groups of three additional busbars 64-66,67-69 is in line with a respective one of the output terminals U, V andW and the aligned busbar 61-63 that is connected to the neutral outputterminal 71. Hence the twelve busbars 56-58, 63-69 are arranged in fourcolumns and in three rows.

[0052] In order to connect the terminal block 51 to provide a seriesstar three phase output arrangement, each of the pairs of busbars 64 and67, 65 and 68, 66 and 69 between a respective one of the three outputterminals U, V and W and a respective one of the busbars 61-63 which isconnected to the neutral output terminal 71, is connected together by arespective connecting link 72-74. In order to alter the outputarrangement from the series star arrangement to a parallel stararrangement, those connecting links 72-74 are removed and replaced byseparate connecting links 75 and 76, 77 and 78, 81 and 82 which areshown chain dotted in FIG. 12 and by which each of the busbars 64-69that is between a power output terminal U, V, W and the respectivebusbar 61-63 that is connected to the neutral output terminal 71 isitself connected by a respective connecting link 15-18, 81, 82 to theadjacent one of the respective power output terminals U, V, W or theneutral terminal busbar 61-63 as can be seen from FIG. 12. Theconnecting links 75-78, 81. 82 which connect the busbars together foreither a series star output arrangement or a parallel star outputarrangement are above the structural panel 51. Hence the connectionarrangement can be changed from one to the other by working from abovethe structural panel 51 and there is no need to provide for access tothe connections of the leads 34 to the busbars below the structuralpanel, which may therefore be permanent Hence there is provided aterminal block 22 which supports the electrical connections between theleads 34 and the output terminals U,V,W of the AC generator which islight in weight and which presents a substantially uninterrupted andelectrically insulating barrier between the working area above thoseterminals U,V,W and the area within the casing 21 below the terminalblock 22 such that there is a minimal risk of tools or debris beingdropped or failing unintentionally into the AC generator during assemblyor refurbishing. Also connection of the generator can be altered betweenseries star and parallel star simply by changing over connections abovethat electrically insulating barrier. Furthermore, the construction ofthe terminal block 22 whereby it comprises six angle members 52 arrangedside by side with upright faces 53 of adjacent angle members 52 abuttingone another and adjacent edges of horizontal sides of those anglemembers 52 abutting one another as well, to form the substantiallyuninterrupted barrier, leads to the resultant panel 51 being a rigidformation. As a result, any tendency for the busbars 56-68 and 61-69that are supported by the panel 51 to be deflected one relative toanother by electromagnetic forces to which they may be subjected,especially under fault conditions externally imposed on the alternatorby the power transmission or distribution system to which it may beconnected, and thus to tend to twist the angle members 52 between whichthey are supported with the possible consequence of short circuiting asadjacent busbars touch one another, is resisted by the angle membersthemselves.

[0053] Although the armature windings 23 described above are perfect lapwindings, it is preferable to use perfect concentric windings. FIG. 13shows armature windings which comprise-twelve sets 83.1-83.12 of perfectconcentric windings. Each set 83.1-83.12 of perfect concentric windingscomprises a single conductor which is bent into four loops, one withinanother so that the four loops can lie substantially ill the same plane,each loop being generally rectangular. The long sides (conductors 36) ofeach loop of a set of windings 83.1-83.12 are laid in a respectiveaxially-extending slot 84 (see FIG. 14) formed in the inner cylindricalsurface of the stator 24 and extend beyond the stator 24 at either endso that the shorter sides of each loop of the stator windings overhangthe stator 24 at the respective end. The four long sides 36 of the loopsof each set 83.1-83.12 that lead in the clockwise sense, with respect tothe other side of that set 83.1-83.12, are laid over the trailing longsides 36 of the next but one set 83.1-83.12 in the clockwise direction.This is so for each and everyone of the twelve sets 83-1-83.12 and is acharacterising feature of “perfect” concentric windings. Each windingset 83.1-83.12 has two output leads 34, one being a neutral lead and theother being a positive output lead.

[0054]FIG. 14 shows that each stator slot 84 within which one long side36 of a loop of a “perfect” concentric winding set 83.1-83.12 is laidupon another, is lined by an insulation 85. Also a Nomex shoe 86 isprovided between the two loop side conductors 36 laid one on the otherin the slot 84. Another such shoe 87 of insulating material, a Nomexpolyester mixture, is laid on the one of those conductors 36 that isnearer the mouth of the slot 84. The latter is narrower than theremainder of the slot 84 and an epoxy glass board 88, which is widerthan the mouth, closes that mouth so as to retain the shoes 86 and 87and the conductors 36 within the slot 84.

[0055] The right hand end of the stator 24, as seen in FIG. 1, is knownas the “Drive End”. The overhanging ends of the sets of windings83.1-83.12 at the “Drive End” comprise the closed ends of all the loopsof the twelve sets 83.1-83.12 of windings at the ends of those sets83.1-83.12 remote from the terminal leads 34 and together comprise acircumferentially-extending annular array of windings 23. Thiscircumferential array is encased in a wide mesh net 89 of lacing cord(as shown in FIG.) and is embraced around its outer surface by anencircling bracing rope 91. The bracing rope 91 comprises an inner coreof pre-stressed linear mono-glass filaments within a woven outer sheathformed by braiding and impregnated with a thermosetting resin afterassembly to comprise a rigid ring which restrains the winding arrayagainst displacement that may otherwise be caused in reaction toelectromagnetic forces induced in the overhanging windings at that endof the stator 24 by high fault levels that may occur in a powertransmission or distribution system into which the AC generator isinstalled. The prestressed linear mono-glass filaments encased in theouter sheath of braided polyester fibres is sufficiently flexible priorto impregnation with the insulating resin, for it to be wrapped aroundthe overhanging portions of the windings 23 so that it closely conformsto the irregular shape of that overhanging portion, it being mouldedinto a rigid ring body having that form after the resin has set.

[0056] The other ends of the loops of each set 83.1-83.12, including theleads 34 of each set 83.1-83.12 similarly overhang from the left handend of the stator 24, as seen in FIGS. 1 and 5. These again are arrangedto form a circumferential array of windings at the left hand end of thestator 24 which is known as the “Non Drive End”.

[0057] The circumferential array of windings 23 at the “Non Drive End”is encased in a wide mesh net of lacing cord and is embraced at its endthat is spaced from the stator 24 by a bracing rope 92. The bracing rope92 is disposed radially inwardly with respect to the cleats 35 becauseof the presence of the latter. Otherwise it is formed in substantiallythe same manner as has been described above for the bracing rope 91 atthe “Drive End”.

[0058] In operation of the AC generator, the coupling plate 26 iscoupled to a fly-wheel of a driving prime mover or engine. Forexcitation of the AC generator its rotor windings are energised eitherby a direct current supply which is supplied to those windings viaterminals on the rotor 25 through brushes and slip rings or, in the caseof a brushless AC generator, by a rectified output of a separate smallexcitor which is usually mounted on the same shaft as the rotor 25. Thelatter has a DC stator winding and a 3-phase or single phase winding onits rotor, the output of which is rectified and fed to the windings onthe rotor 25. This excitation current, whether it is a separate DCsupply or a rectified output of an exciter is a current of lowerstrength than the output of the AC generator.

[0059] The driving prime motor is actuated to rotate the rotor 25 withinthe stator 24. The output current is generated in the stator windings 23by mutual induction in the usual way and is led through the leads 34 tothe terminals U, V, W of the terminal block.

[0060] The fan 27 rotates with the rotor 25, draws air through thestator 24 from the remote end thereof and discharges that air throughthe discharge passages 32 formed by the volute casing 30. Use of thevolute casing 30 improves the cooling by increasing the volume of airthat is drawn through the stator 24 by the fan 27 for discharge throughthe discharge passages 32 formed by the volute casing 30. Furthermorethe arrangement of the blades 31 whereby they are oblique to the radialso that they trail the radial, contributes to this arrangement.Moreover, the tapering of the tips of the blades 31 leads to a lowernoise output than has been found to be the case where the blades hadtips which were substantially parallel to the axis of rotation.

[0061] The air that is drawn through the stator 24 by the fan 27 is alsodrawn into the stator 24 around and through the leads 34 that are ledaround the six axially spaced circumferentially extending tracks formedby the circumferential array of cleats 35, those leads 34 beingsupported in free space by the cleats 35 with which they cooperate toform a grid structure as has been described above, the interstices ofthat grid structure serving as ventilation spaces through which that airis drawn. This enhances the ventilation of those leads 34 and furtherimproves the cooling of the AC generator. There is some improvement incooling with perfect lap winding3, so that the rating of the ACgenerator would be improved, but the conjoint effect of the arrangementof the leads 34 so they extend around the six axially spacedcircumferentially extending tracks with the use of perfect concentricwindings gives even better cooling of the windings and hence bettervoltage and current balance in the windings of the stator 24. This leadsas a result to an increase in the power density or-rating of the ACgenerator. The improved cooling that follows from the use of the volutecasing 30 with the blades 31 that are oblique to the radial so that theytrail the radial as described, together with that, that follows from theconjoint effect of the arrangement of the leads 34 in six axially spacedcircumferentially extending tracks and the use of perfect concentricstator windings, leads to an increase of between 15 and 20% in powerdensity.

[0062] The arrangement of the terminal block 22 results in the physicalsupport for the metal busbars 56-59, 64-69 which conveniently are formedof a tin plated copper, being provided by the insulating material whichis considerably more light weight than the conventional weldedstructure.

[0063]FIGS. 15 and 16 show a modification of the AC generator describedabove with reference to FIGS. 1 to 14. Parts of the generator shown inFIGS. 15 and 16 which are similar to corresponding parts of thegenerator shown in FIGS. 1 to 14 are identified by the same referencecharacters. The generator shown in FIGS. 15 and 16 has “perfect”concentric windings 83 as have been described above with reference toFIGS. 13 and 14.

[0064]FIG. 15 shows a circumferential array of six cleats 93 which aremounted on the curved winding portions that comprise the ends of thetwelve sets 83.1-83.12 of winding portions that project from the “NonDrive End” of the stator 24. FIG. 16 shows that each of those cleats 93is similar to the cleat 35 that has been described above with referenceto and as shown in FIG. 8, except that the back portion 39 of the cleat93 projects axially beyond the prongs 41 at the end thereof remote fromthe tongue 44 to form a shoulder 94 with the prong 41 that is furthestfrom the tongue 44. The shoulders 94 of each of the circumferentialarray of cleats 93 provide a seat for a solid ring 95 of copper (shownchain dotted in FIG. 5) which rests thereon whereby the ring 95 issupported by the circumferential array of cleats 93.

[0065] The ring 95 is not a complete circle but extends over about 350°,the spaced ends of the resultant loop being at the top. Each of theneutral leads of the windings 23 is electrically connected to the ring95 so supported on the annular array of cleats 93. To ensure a goodelectrical connection, the end of each such neutral lead is bared byremoving the enamel coating to expose copper whereby to provide a goodcopper-copper contact. The ring 95 is retained upon its seat on eachcleat 93 by the strap 47 that is passed around it.

[0066] Each of the depending portions of the six narrower busbars 64-69shown in FIG. 11 and each of the load output terminals 56-58 has arespective pair of the positive output leads 34 connected to it. Twoneutral connectors 96 and 97 are connected to one of the dependingportions of the neutral busbars 61-63 (indeed the neutral busbars 61-63may be arranged so that only one of them depends below the panel 51).Each of those neutral connectors 96 and 97 is connected to a respectiveend of the open loop that comprises the solid ring 95.

We claim:
 1. An alternating current machine comprising a rotorjournalled for rotation within a stator comprising stator windings whichare gathered together into an annular array at one end of the stator,the stator windings having terminal leads which are guided aroundrespective circumferentially extending paths and coupled to terminalmeans, there being a plurality of such circumferentially extendingpaths, each at locations which are spaced axially from other such pathswith respect to the stator, the improvement comprising a circumferentialarray of supporting and guiding means at said one end of the stator forguiding said terminal leads around said paths, the supporting andguiding means being spaced from one another circumferentially such thatsaid terminal leads supported and guided thereby extend between them infree space and ventilation gaps are formed between adjacent terminalleads and supporting and guiding means whereby cooling of the terminalleads is enhanced by air flow through those ventilation gaps.
 2. Analternating current machine according to claim 1 , wherein each statorwinding lead is an integral continuation of a conductor which forms arespective stator winding.
 3. An alternating current machine accordingto claim 1 , wherein the stator winding terminal leads that comprise theends of a respective stator winding are led together for connection torespective terminals of a terminal block from a location which is in thesame notional plane that is normal to the axis of rotation of the rotorwithin the stator.
 4. An alternating current machine, according toclaims 1, wherein each of the supporting and guiding means of said arraycomprises an axially orientated member which is formed of electricallyinsulating plastics material and which is operable to guide the discretebundles side by side along the respective paths between the adjacentmembers of the array.
 5. An alternating current machine according toclaim 4 , wherein each member comprises an elongate back portion withintegral prongs which project laterally therefrom so that it has theform of a comb, the prongs projecting outwardly with respect to the axisof the stator and serving as spacers which space juxtaposed ones of theterminal leads apart and react electromagnetic forces which act to urgetowards them either of the terminal leads they separate.
 6. Analternating current machine according to claim 5 , wherein the prongsare shaped so that the nearer sides of juxtaposed prongs convergetowards the ends of the prongs remote from the back portion, the mouthsformed between those ends of juxtaposed pairs of the prongs being sizedsuch that a terminal lead can be fitted into the intervening spacesbetween each juxtaposed pair of prongs with a snap action.
 7. Analternating current machine according to claim 5 , wherein each memberis provided with means fitted to the ends of its prongs for bracing theleads into it.
 8. An alternating current machine according to claim 7 ,wherein said means which are operable to brace the leads into eachmember are part of an elongate flexible rod member which, in addition tofunctioning to brace the leads into the respective member, alsocomprises a strap portion which is passed under the back portion of therespective member, remote from the prongs, and under bundles ofconductors that comprise portions of the stator windings that have beenturned around at said one end of the stator, whereby the respectivemember is strapped to the stator windings by the strap portion.
 9. Analternating current machine according to claim 1 , wherein the rotor iscoupled with a fan for conjoint rotation, the fan being within a casingand being operable to cause air flow through the stator from said oneend, that air flow being drawn into the stator through the ventilationgaps formed between juxtaposed terminal leads and adjacent supportingand guiding means at said one end of the stator, the casing cooperatingwith the fan to provide a conduit for discharge air flow from the fan.10. An alternating current machine according to claim 9 , wherein theconduit is in the form of a volute whereby its area increasesprogressively in the downstream direction.
 11. An alternating currentmachine according to claim 9 , wherein there are two sets of conduitsdiametrically opposed one with respect to the other and oriented todischarge in opposite directions.
 12. An alternating current machineaccording to claim 10, wherein the fan is a radial flow fan which hasblades which project from the hub at an angle which is oblique to theradial whereby those blades trail the radial.
 13. An alternating currentmachine according to claim 10 , wherein the tip of each blade is angledwith respect to the axis of rotation of the fan whereby it diverges fromthe surrounding casing wall in the direction which is parallel to theaxis of rotation and which extends away from said one end of the stator.14. An alternating current machine according to claim 10 , wherein thefan is bolted onto the rotor so as to be readily replaceable.
 15. Analternating current machine according to claims 1 to 14 , wherein saidterminal means comprise a structural panel formed of an electricallyinsulating structural material, busbars which extend through and whichare supported by the panel with minimal clearance therearound, thebusbars having terminals formed at either end, said terminal leads beingconnected to the busbar terminals that are on the same side of the panelas are the stator windings, the arrangement being such that the panelsubstantially closes the surrounds of the busbars around which it isclose fitted.
 16. An alternating current machine according to claim 15 ,wherein the structural panel comprises abutting juxtaposed elongatemembers.
 17. An alternating current machine according to claim 16 ,wherein each elongate member is an angle member, upstanding portions ofthe juxtaposed angle members being in face to face abutment with thebusbars sandwiched between them and the other edges of the angle membersabutting also, each busbar extending through a respective recess formedin one of the abutting faces in the juxtaposed angle members.
 18. Analternating current machine according to claim 15 , wherein the busbarscomprise three power output busbars and, for each such power outputbusbar, a respective neutral and a pair of spaced busbars, which arelocated between the respective power output and neutral busbars fromwhich they are spaced, and linking means operable selectively to connectsaid pair of spaced busbars together for a series star connection and toconnect one busbar of each said pair to the adjacent one of the poweroutput and neutral busbars and to connect the other busbar of each saidpair to the other of the power output and neutral busbars for a parallelstar connection, said connections by said linking means being made onthe side of said structural panel opposite to the ends of the busbars towhich said terminal leads are connected.
 19. An alternating currentmachine according to claims 1, wherein the neutral terminal leads areconnected to a solid ring of a good electrically conducting materialwhich in turn is connected to said terminal means.
 20. An alternatingcurrent machine according to claim 19 , in which said terminal meanscomprise a structural panel formed of an electrically insulatingstructural material, busbars which extend through and which aresupported by the panel with minimal clearance therearound, the busbarshaving terminals formed at either end, said terminal leads beingconnected to the busbar terminals that are on the same side of the panelas are the stator windings, the arrangement being such that the panelsubstantially closes the surrounds of the busbars around which it isclose fitted, wherein said ring is connected to a neutral busbar belowsaid panel.
 21. An alternating current machine according to claim 19 ,wherein said ring is open ended and both of its ends are connected tosaid neutral busbar by respective connecting means.
 22. An alternatingcurrent machine according to claim 19 , wherein said ring is supportedby said supporting and guiding means.
 23. An alternating current machineaccording to claim 22 , in which each member comprises an elongate backportion with integral prongs which project lateraly therefrom so that ithas the form of a comb, the prongs projecting outwardly with respect tothe axis of the stator and serving as spacers which space juxtaposedones of the terminal leads apart and react electromagnetic forces whichact to urge them towards either of the terminal leads they separate,wherein said ring in supported in contact with the one of said prongs ofeach said member that is the furthest from the stator.
 24. Analternating current machine according to claim 23 , in which each memberis provided with means fitted to the ends of its prongs for bracing theleads into it and said means which are operable to brace the leads intoeach member are part of an elongate flexible rod member which inaddition to functioning to brace the leads into the respective member,also comprises a strap portion which is passed under the back portion ofthe respective member, remote from the prongs, and under bundles ofconductors that comprise portions of the stator windings that have beenturned around at said one end of the stator, whereby the respectivemember is strapped to the stator windings by the strap position, whereinsaid ring is held so supported in contact with said one prong of eachsaid member by the respective flexible rod member by which that memberis strapped to the stator windings.
 25. A terminal arrangement for leadsfrom stator windings of an alternating current machine, comprising anarray of structural members and busbars which extend through and whichare supported by the array, the busbars having terminals at either end,wherein the improvement comprises the structural members of the arraybeing formed of an electrically insulating structural material and beingin face to face abutment whereby they form a structural panel whichpresents a substantially uninterrupted surface, each of the busbarswhich extends through and which is supported by the panel being a closefit within a respective through passage, the through passage beingformed by appropriate grooves in abutting faces of the structuralmembers, the arrangement being such that the panel substantially closesthe surrounds of the busbars around which it is close fitted.
 26. Aterminal arrangement according to claim 25 , wherein each structuralmember is elongate and is an angle member, upstanding portions of thejuxtaposed angle members being in face to face abutment with the busbarstherebetween close fitted in such grooves which are formed thereby andthe other edges of the angle members abutting also.
 27. A terminalarrangement according to claim 25 , wherein the busbars comprise threepower output busbars and, for each such power output busbar, arespective neutral and a pair of spaced busbars which are locatedbetween the respective power output and neutral busbars from which theyare spaced, and linking means operable selectively to connect said pairof spaced busbars together for a series star connection and to connectone busbar of each said pair to the adjacent one of the power output andneutral busbars and to connect the other busbar of each said pair to theother of the power output and neutral busbars for a parallel starconnection, said connections by said linking means being made on theside of said structural panel opposite to the ends of the busbars towhich stator winding terminal leads are connected.
 28. An alternatingcurrent machine comprising a rotor journalled for rotation within astator, the stator comprising stator windings which project from one endof the stator for connection to a terminal arrangement, and the rotorbeing coupled with a radial flow fan for conjoint rotation, the fanbeing within a casing and being operable to cause air flow through thestator from said one end, the casing cooperating with the fan to providea conduit for discharge of air flow from the fan, the conduit being inthe form of a volute whereby its area increases progressively in thedownstream direction, wherein the improvement comprises the fan havingblades which project from the hub at an angle which is oblique to theradial.
 29. An alternating current machine according to claim 28 ,wherein there are two such conduits diametrically opposed one withrespect to the other and oriented to discharge in opposite directions.30. An alternating current machine according to claim 28 , wherein thetip of each blade is angled with respect to the axis of rotation of thefan whereby it diverges from the surrounding casing wall in thedirection which is parallel to the axis of rotation and which extendsaway from said one end of the stator.
 31. An alternating current machineaccording to claim 28 , wherein the fan is bolted onto the rotor so asto be readily replaceable.